Theresa May has more than a touch of Teflon about her (her record as Home Secretary—interior minister—was notable mostly for broken promises on immigration and displays of petty and not so petty authoritarianism). Even more than that that she has had the luck to be in the right place at the right time. When the aftermath of the Brexit vote (and Michael Gove’s clumsy conspiracies) reduced the top of the Tory hierarchy to chaos, she was there to pick up the pieces, the leadership and the premiership. Up to then she had only distinguished herself by her discretion (she had been the lowest of low-key Remainers), her skill in a political knife-fight, and her remarkable ability to portray herself as competent, something for which there is, in truth, not too much evidence.

And then she had the advantage of an opposition led by Jeremy Corbyn, a dim-witted leftist fanatic so repulsive that even some of Labour’s most loyal voters cannot bring themselves to support him.

It’s likely that she will win next month’s election by a (very) solid majority.

But no majority is forever and there are signs that May, who has clearly confused luck with achievement, has forgotten that. In her manifesto she has taken direct aim at the elderly (and, effectively, their children), a strategy that she will be able to get away with for now, but which is likely to linger in British political memory for a long time – and not in a good way.

The Tory manifesto says, in effect, that people who need care in old age will have to pay for every penny of it – no matter how big the costs – if they have more than £100,000 in assets, which will be protected. Payment can be deferred until after death, but there’s no escaping it. If you have a home worth, say, £216,000 (the national average), own it outright, and need to be looked after for a long time, you may have to cough up £116,000.

Currently, it’s true, anyone with assets of over £23,250 has to pay for the full cost of their care (family homes are included in totalling assets for those in residential care). But the government, at least until today, was going to introduce a cap of £72,000 in 2020 – based on Sir Andrew Dilnot’s proposals made in the coalition years. Now people risk having to pay far more than that.

Let’s imagine two 80-year-old widows who live next-door to each other somewhere in the south of England. Their properties are both worth £312,000 and they have another £10,000 in other assets, so a total of £322,000 each. Happily, they both live till 95. Unhappily, one of them suffers dementia for 10 years, and soon needs round-the-clock care. The other widow is healthy and reasonably active until the very end of her life.

Under the new Conservative plans, the one who is healthy until the end of her life will leave her estate completely intact to her loved ones. The one who needs all that care, however, will be billed up to £222,000. Over 10 years, at current costs for care, that’s very plausible: the BBC estimates that nursing care costs £1,000 a week; home care £16.70 an hour; ordinary residential care £700 a week.

Having such assets is not as rare as you might think. According to the English Housing Survey, 78pc of over-65s are owner-occupiers. A large proportion of those will have paid off 25-year mortgages.

So is the May proposal remotely fair? It doesn’t seem so to me. This is effectively a massive inheritance tax – but only on those who are ill in old age and need to be looked after. People are calling it a ‘dementia tax’ on Twitter, which I suspect will catch on. As Rachel Sylvester points out, ‘It’s a condition lottery – if you have cancer you are treated free on NHS, if Alzheimer’s you pay for all care.’

“They propose to build a system maintaining the current huge incentives to divest wealth before any need to access social care. Families are best off if they give away wealth to their offspring early, if they spend the money on cruises, or even on a lifestyle that is more likely to result in a rapid death.”

Whatever happened to the Conservative belief that inheritance was a good thing? To the idea that building up assets with your children or grandchildren’s futures in mind was one of the very noblest, not to mention the most human and natural, aims in life? The Bow Group say today’s announcement is ‘likely to represent the biggest stealth tax in history’. It’s hard to think of another one that could destroy assets built up over a lifetime in just a few short years.

The Dilnot proposals to cap an individual’s care costs have been replaced by something worse. Wouldn’t it have been possible – and fairer and better – to engineer pooled risk among the general population, providing a kind of social care insurance? We’re all going to get old one day.

Under the new rules, if middle-class home-owners want to hand on money to their loved ones, they will just have to make sure they die the right way. Get dementia, lose most of your wealth. Die suddenly of a heart attack, your family will be looked after. Is the Conservatives’ drastic solution really the best they could come up with?

Beyond its basic cruelty, May’s dementia tax is an attack on thrift, a tax on achievement and an assault on the basic human instinct to pass something on to the next generation. Mrs. Thatcher used to reject this sort of means-testing approach (which sadly can be seen over here too). And she did so on moral, political and societal grounds. The Conservative Party is clearly not what it was.

One lifelong (and elderly) Tory said to me yesterday that, after reading May’s proposals, he was briefly tempted to vote Labour, but then “Corbyn’s a bloody Trot….”